Auxiliary fuel tank

ABSTRACT

A fuel system for an engine includes a fuel line that delivers fuel from a main fuel tank to the engine and a first control device that releases a flow of the fuel from the main fuel tank into the fuel line. An auxiliary fuel tank is connected to the fuel line, and a second control device controls a flow of the fuel between the auxiliary fuel tank and the fuel line. After the fuel is released from the main fuel tank into the fuel line, the second control device fills the auxiliary fuel tank with the fuel from the main fuel tank.

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/839,213, filed on Aug. 21, 2006, and is a Continuation-In-Part(CIP) of U.S. patent application Ser. No. 11/842,923, filed on Aug. 21,2007, both of which are herein incorporated by reference in theirentirety.

BACKGROUND

Industrial vehicles such as forklift trucks, man-lifts and sweepers, mayutilize liquid propane (LP) engines to provide vehicle traction,hydraulics and other functions. LP fuel, while typically provided as aliquid under pressure of a fuel tank, becomes substantially vapor byvolume as the fuel is used up. Fuel level sensors that rely on fuellevel in an LP tank, or on tank pressure, provide for an insufficientamount of warning time as the tank is nearing empty. Vehicle operatorscomplain the low LP fuel warning light and/or audible alarm does notcome on soon enough to provide adequate time to reach a refuelingstation or complete a task. Under some circumstances, the warning lightcomes on and the liquid propane gas engine stalls shortly or immediatelythereafter from lack of adequate fuel. The pressure at which liquid LPturns to vapor in the tank varies under different operating conditions,not least of which is an ambient temperature.

One challenge with LP fuel level sensing on LP engine powered systems iscaused by the fact that most are refueled by exchanging fuel tanks.Incorporating a fuel level sensor gauge that is visible to the operatorin all these exchange tank applications is expensive. Such fuel levelsensor gauges require additional electrical connections (e.g. for thetruck dash display) when exchanging fuel tanks and result in reliabilityproblems.

A pressure switch based low LP fuel warning system includes a pressureswitch in the fuel supply line and an indicator light on the dash and/oraudible alarm. The switch generally activates when the fuel systempressure drops below some threshold, resulting in a short warning to theoperator. However, during cold weather applications of 35 degreesFahrenheit or lower, the propane vapor pressure may be lower than thethreshold even if the tank is full. This means the low fuel indicatorlight will stay on even if the tank is full. Additionally, pressureswitch based low LP fuel warning systems include moving parts which tendto fail or require servicing over time.

On some conventional low fuel warning systems, if the tank on thevehicle runs out of liquid fuel, the gauge will still show a partialfuel level. The low fuel warning will only come on when the vaporpressure is low enough to activate the pressure switch. The operator,who planned on working with half a tank of fuel is suddenly left withoutany vehicle power. Down time caused by the truck being stranded whenrunning out of fuel, or leaving a task partially finished due to lowfuel, costs money. It also contributes to service calls to the servicedepartment.

The energy content of liquid fuel in a given volume is slightly affectedby temperature. However, fuel energy content of fuel vapor issignificantly dependant upon temperature. Equivalent energy content ofliquid propane gas is 270 times more than propane vapor. Therefore asmall volume of liquid propane gas has more energy content than a largetank of propane vapor. Conventional low fuel warning designs rely on avapor volume reserve. If a tank is full of propane vapor, it does nothave much energy content to run a truck, especially in cold weather.

Conventional low fuel warning systems normally depend upon decreasingvapor pressure to activate a pressure switch that turns on a warninglight or an audible alarm. Depending on the ambient temperature, fuelconsumption rate, the tank size, and pressure switch setting, therun-time after a low fuel warning light illuminates is approximately twoto four minutes. If the truck is operated in very low temperatureconditions, the propane vapor pressure can be so low that the low fuelwarning light stays on all the time.

The present invention addresses these and other problems.

SUMMARY OF THE INVENTION

A fuel system for an engine is herein disclosed. The fuel system maycomprise a fuel line configured to deliver fuel from a removable mainfuel tank to the engine and a first control device configured to releasea flow of the fuel from the main fuel tank into the fuel line. Anauxiliary fuel tank may be connected to the fuel line, and a secondcontrol device may be configured to control a flow of the fuel betweenthe auxiliary fuel tank and the fuel line. After the fuel is releasedfrom the main fuel tank into the fuel line, the second control devicemay fill the auxiliary fuel tank with the fuel from the main fuel tank.

An apparatus is herein disclosed. The apparatus may comprise means fordelivering fuel from a removable main fuel tank to an engine, and meansfor releasing a flow of the fuel from the main fuel tank into the meansfor delivering. The apparatus may comprise means for storing anauxiliary fuel supply, and means for controlling a flow of the auxiliaryfuel supply between the means for storing and the means for delivering.The apparatus may further comprise means for filling the means forstoring with the fuel from the main fuel tank after the flow of fuel isreleased from the main fuel tank into the means for delivering.

A method is herein disclosed. The method may comprise delivering fuelfrom a removable main fuel tank to an engine, and releasing a flow ofthe fuel from the main fuel tank into a fuel line. The method mayfurther comprise controlling a flow of the fuel between an auxiliaryfuel tank and the fuel line, and filling the auxiliary fuel tank withthe fuel from the main fuel tank after the flow of fuel is released fromthe main fuel tank into the fuel line.

A fuel sensor for detecting a low fuel condition in a motorized vehicleis herein disclosed. The fuel sensor includes an effective signal pathconfigured to detect a fuel, and a fuel reservoir configured to beconnected to a fuel line. The fuel sensor further includes a housingcontaining the effective fuel path that is located adjacent the fuelreservoir. The fuel reservoir is configured to trap the fuel in a liquidphase as it is being transmitted through a fuel line and past thehousing for detection by the effective signal path.

A low fuel warning system of a motorized vehicle is herein disclosed.The low fuel warning system includes a fuel line configured to transportfuel between an inlet port and an outlet port and a reservoir locatedintermediate to the inlet port and the outlet port, wherein thereservoir is configured to collect the fuel in a liquid state. The lowfuel warning system further includes a fuel sensor located adjacent thereservoir and configured to detect the liquid state of the fuel and aprocessor in communication with the fuel sensor. The processor isconfigured to monitor a low fuel condition in the fuel line according toinformation received from the fuel sensor.

A method of monitoring a low fuel condition in a motorized vehicle isherein disclosed, including receiving signals from a fuel sensor,determining a number of the signals received from the fuel sensor, andidentifying the low fuel condition when the number of received signalsexceeds a threshold value. The method further includes alerting avehicle operator of the low fuel condition and commanding a low fuelmode of operation of the motorized vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a low fuel warning system for a motorized vehicle.

FIG. 2A illustrates an example fuel tank maintained in a verticalorientation.

FIG. 2B illustrates the example fuel tank of FIG. 2A maintained in ahorizontal orientation.

FIG. 3A is a simplified view of a fuel sensor.

FIG. 3B illustrates the fuel sensor of FIG. 3A immersed in a liquid.

FIG. 4 illustrates a plan view of a sensor housing.

FIG. 4A illustrates a first cross-sectional view of the sensor housing.

FIG. 4B illustrates a second cross sectional view of the sensor housing.

FIG. 5 illustrates a fuel sensor positioned below a reservoir.

FIG. 6 illustrates a fuel sensor located on an auxiliary fuel line.

FIG. 7 illustrates a fuel sensor positioned above a reservoir.

FIG. 8 illustrates an alternate embodiment of a fuel sensor.

FIG. 9 illustrates an algorithm for detecting a low fuel condition.

FIG. 10 illustrates an auxiliary fuel tank system.

FIG. 11 illustrates a relationship of vehicle run time estimations,vapor pressure and ambient temperature of a liquid propane fuel system.

FIG. 11A is a table illustrating example operating conditions used inthe run time estimations of FIG. 11.

FIG. 12 illustrates a example method of monitoring a low fuel condition.

FIG. 13 illustrates a further embodiment of an auxiliary fuel tanksystem

DETAILED DESCRIPTION

FIG. 1 illustrates a low fuel warning system 10 for a motorized vehicle(not shown). The low fuel warning system 10 may include a liquid drawtype liquid propane (LP) fuel system including a fuel sensor 30 that isconfigured to detect the presence of liquid, vapor, or any phasecombination of propane in a pipe, fuel supply line, or container. Thelow fuel warning system 10 is illustrated as showing componentsconnected by lines, however these lines are provided for illustrativepurposes only, and may be understood to represent fuel lines, electricalconnections, or communication between components.

The low fuel warning system 10 may be incorporated in an enginemanagement system that is controlled by an on-board computer, processoror controller 200. The controller 200 may receive input from a pressuretransducer 16, a tank temperature sensor 21, the fuel sensor 30, andvarious other components of the engine management system. The controller200 may provide input to, or control, a vehicle horn 12, a low fuelindicator 6, an engine 15, etc.

Various switches may be provided that are under control of thecontroller 200 or that are pressure activated. A pressure switch S1 isshown connected intermediate the fuel sensor 30 and the pressuretransducer 16. A sight glass 18 may be provided near the fuel tank 20,for example, to make visible the fuel in the fuel line during testing.Otherwise, the sight glass 18 is not typically provided in the low fuelwarning system 10. A sensor output switch S2 is shown intermediate tothe fuel sensor 30 and the controller 200. Toggle switch S3 is shownintermediate a horn 12 and the controller 200. An audible alarm 7 mayprovide a warning of a low fuel condition, including a final warning ofimminent fuel exhaustion. The low fuel indicator 6 and/or the audiblealarm 7 may be contained in a sensor indicator light box 4. The low fuelindicator 6 is shown as including a switch S4. The low fuel warningsystem 10 may include pressure or temperature sensing switches andsensors which may be configured to trigger additional warnings after thelow fuel indicator 6 is first activated, and before the fuel tank 20runs out of fuel.

The battery 8 may provide power to the horn 12 and the sensor indicatorlight box 4, as well as other electrical components in the low fuelwarning system 10, such as the controller 200. A filter/regulator 14 isshown connected to the fuel line between the engine 15 and an LP lockoff11. The fuel tank 20 may include a tank heater 27, that is configured tooperate according to changes in ambient temperature, fuel temperature,fuel pressure, fuel level, or various other operating parameters.

The low fuel warning system 10 may include a low fuel indicator 6 (e.g.a light and/or an alarm) to make a vehicle operator aware of a low fuelcondition. The low fuel warning system 10 may utilize the LP lockoff 11to initiate a low fuel mode of operation to prevent the starter motoroperating with no fuel to the engine leading to starter motoroverheating and battery 8 discharge and/or to limit engine rpm. Themultiple restart practice is a common occurrence in some operations,that otherwise may use the starter motor to get the vehicle to moveafter the vehicle runs out of LP fuel.

The fuel sensor 30 may incorporate a filtered output signal to prevent aflickering or intermittent notification of the low fuel indicator 6resulting from an instantaneous vapor reading. This may be accomplishedby programmable output signal logic. In one embodiment a microprocessoris incorporated into the fuel sensor 30, whereas the fuel sensor 30 maybe controlled by the controller 200 in some applications or otherembodiments. The low fuel indicator 6 may be provided in a dash displayof the vehicle. In one embodiment, an aftermarket configuration vaporsensor based low fuel warning system may be implemented whichincorporates it's own warning light and/or audible alarm to ensurefunctional compatibility on all forklifts or other LP engine poweredvehicles or equipment.

FIG. 2A illustrates an example fuel tank 20 maintained in a verticalorientation. The fuel tank 20 may be an exchangeable LP fuel tankincluding an internal fuel supply tube 22.

The low fuel warning system 10 of FIG. 1 may take advantage of theliquid fuel 25 under the fuel tank's fuel supply tube inlet 23, as wellas the pressurized propane vapor 24 in the tank 20, which combine toserve as an internal low fuel reservoir supply. This liquid fuel 25 mayprovide a minimal reserve operational time regardless of ambient oroperating temperature. The LP fuel system typically starts running onvapor when the liquid fuel level 25 drops below the fuel supply tubeinlet 23, and the liquid fuel 25 is subsequently converted to propanevapor 24.

FIG. 2B illustrates the example fuel tank 20 of FIG. 2A maintained in ahorizontal orientation. A pool of the liquid fuel 25 is shown locatedbeneath the fuel supply tube inlet 23 of the internal fuel supply tube22, similarly as described with reference to FIG. 2A.

The low fuel warning system 10, including the fuel sensor 30, mayprovide additional low fuel warning time after the liquid fuel 25 is nolonger in the fuel line 35. Fuel from this reservoir of pressurizedvapor 24 inside the fuel tank 20 can result in additional low fuelwarning time. Warmer weather can increase the tank vapor pressure andresult in a longer run time after liquid fuel 25 runs out.

FIG. 3A is a simplified view of a fuel sensor 30. In one embodiment thefuel sensor 30 includes optic refraction sensor technology. The fuelsensor 30 is illustrated as being mounted in a fuel line 35. The fuelsensor 30 may include an emitter 32 and a receiver 34, and in oneembodiment does not include any moving parts. This may increasereliability of the fuel sensor 30 as well as the low fuel warning system10. The emitter 32 may be configured to transmit a signal 38, whereasthe receiver may be configured to receive or identify the signal 38. Thesignal 38 may form a light path within the fuel sensor, such as within asensor cone 37. The sensor cone may include one or more lens 36. Whenthe fuel sensor 30 is immersed in a vapor or gas, the signal 38 isreflected by the lens 36 such that the signal remains inside of thesensor cone 37, essentially at full strength.

FIG. 3B illustrates the fuel sensor 30 of FIG. 3A immersed in a liquidsuch as liquid fuel 25. Some of the signal 38 may be absorbed by, orrefracted into, the liquid fuel 25 that is in contact with the lens 36,such that the signal 38 that is received by the receiver 34 is lessstrong as compared to the fuel sensor 30 illustrated in FIG. 3A. Arefracted signal 39 that is emitted into the liquid fuel 25 maytherefore not be received by the receiver 34. In one embodiment, thereceiver 34 identifies a liquid, vapor, or combined liquid and vapor(i.e. two phase) state of the LP fuel in the fuel line 35 according tothe strength of the received signal 38.

While the fuel sensor 30 may be configured to detect the differencebetween liquid and vapor propane, in some cases this may result in aflickering indicator light condition due to irregular flow of LP fuel inthe fuel line 35. The irregular flow of LP fuel may result from varyingdemands of the engine 15 (FIG. 1), for example idle versus full throttleoperating conditions, as well as vapor pockets that may form in the fuelline 35. A microprocessor or controller, such as the controller 200 ofFIG. 1, may be configured to filter the signal 38 via a light activationlogic sequence. The light activation logic sequence is illustrated inFIG. 9, and described in detail, further herein.

FIG. 4 illustrates a plan view of a sensor housing 40. The sensorhousing may be attached to the fuel line 35 (FIG. 3A, 3B). A first crosssection of the sensor housing 40 is shown taken with respect to axis A-Aand further illustrated in FIG. 4A. A second cross section of the sensorhousing 40 is shown taken with respect to axis B-B and furtherillustrated in FIG. 4B.

FIG. 4A illustrates the first cross-sectional view of the sensor housing40 including the fuel sensor 30. The housing 40 may be attached orconnected to the fuel line 35. The housing 40 may include or beconnected to a first port 44 and a second port 45 of the fuel line 35.In one embodiment, the first port 44 is configured in an approximatelyhorizontal orientation, whereas the second port 45 is oriented in anapproximately vertical orientation. In one embodiment, the first port 44is an outlet port and the second port 45 is an inlet port.

FIG. 4B illustrates a second cross sectional view of the sensor housing40, including the emitter 32 and the receiver 34. The effective signalpath 48 of the fuel sensor 30 may identify a path of the signal 38 ofFIG. 3A. A restrictive gap 46 (FIG. 4A) may be provided between the lens36 and the housing 40 to facilitate contact of any amount of liquid fuelto contact the effective signal path 48, for example during a low fuelflow situation. By restricting the flow of fuel past a sensitive part ofthe lens 36, this helps to avoid generating erroneous vapor signals thatmay otherwise occur if the lens 36 is instead in contact with vapor. Inone embodiment, this can be accomplished by locating the lens 36 closeto the housing 40.

The restrictive gap 46 may be big enough to allow debris to pass throughand not cause excess flow restriction to the LP fuel. The restrictivegap 46 may be small enough to ensure liquid fuel contacts the lens 36 ina low flow situation. In one embodiment, the restrictive gap 46 isapproximately 0.05 inches. The size of the restrictive gap 46 may dependupon the location of the sensor's detection zones or effective signalpath 48. Flattening the tip of the lens 36 and minimizing the housingclearance from the lens surface may provide an ability to furthercontrol the amount of fuel flow which goes through this sensitive crosssection area. This may allow the fuel to flow past the sides of the lens36 in regions where the signals 38 or effective signal path 48 exist.

The restrictive gap 46 (FIG. 4A) or restriction zone located between thesensor housing 40 and the lens 36 results in any residual fuel dropletsclearing off from the lens 36 sooner when the fuel supply changes from aliquid to a vapor. High velocity propane vapor blows past the lens 36 inthis restrictive gap 46 causing the residual fuel droplets to movedownstream. This reduces the chance of the fuel sensor 30 producing anerroneous output due to residual liquid fuel droplets remaining on thelens 36.

Intermittent fuel flow intervals that can occur during idle conditionscan vary from constant flow out of the fuel tank 20 to no flow for a fewseconds depending upon engine size and tank configuration. A predictableliquid volumetric siphon effect of a 100% fluid column from the fueltank 20 to the engine 15 may not exist due to the generation of vaporbubbles & vapor pockets within the fuel line 35. Instead, during idleconditions with a full or partially full tank 20, the fuel tank 20“burps” out liquid fuel in seemingly random time intervals as describedabove. To compensate for this, a sensor sampling time interval can beprogrammed to be a bit longer than the longest “burp” interval for theapplication. Other methods such as locating the sensor lens 36 in aliquid fuel reservoir inside the fuel sensor 30 or the fuel line 35 mayalso be used to address the intermittent flow issue, as describedfurther herein. In one embodiment, the fuel sensor 30 is located near orat the vaporizer 110 (FIG. 10) to identify a lower liquid flow.

By configuring the port 44 in a substantially horizontal orientation andthe port 45 in a substantially vertical orientation, false vaporreadings may be avoided. Liquid fuel may be allowed to drain into theport 45, whereas vapor may be vented around the lens 36 and out the port44.

The location of the emitter 32 and receiver 34 (FIG. 3) may be orientedsuch that the effective signal path 48 (FIG. 4B) resides at the sides ofthe lens 36 where the maximum flow restriction occurs. The effectivesignal path 48 may be located above or below the reservoir 50. In oneembodiment, the beam plane is approximately perpendicular to the axes ofthe inlet and outlet ports 45, 44. This ensures liquid fuel 25 contactsthe sensitive part of the lens 36 instead of bypassing it.

The housing 40 and sensor lens 36 may be arranged such that any liquiddroplet would drain out and any vapor bubble would vent instead of beingtrapped, causing erroneous signals. This may be accomplished byoffsetting the downstream port axis from the lens axis. Increasing thebore size of the inlet and outlet ports 45, 44 may also extend the innerdiameter of the fuel line 35 to the edges of the reservoir 50 locatedbetween the lens 36 and the housing 40.

Liquid fuel flow may be very low and intermittent during idleconditions. In some cases liquid fuel 25 trickles through the bottom ofthe fuel line 35 when a large vapor pocket exists in the fuel line 35.Fuel sensor performance can also be affected by the location of the fuelsensor 30. Sometimes there are vapor pockets in the higher and morevertical sections of the fuel supply line 35. Also, the amount of vaporin the fuel may increase near the vaporizer 110 (FIG. 10) or other hotsupply line components which cause vapor bubbles to form. In oneembodiment, the fuel sensor 30 is located in a low part of the fuel line35 away from hot supply line components.

The fuel sensor 30 and housing 40 may include a ¼NPT pipe fitting and/orSAE 45 plumping connection, for example, that can be arranged to bestraight or at an angle (e.g. between 45 degrees and 90 degrees). Thelens 36 may provide a predetermined angle of refraction according to thetype of fuel, such as LP fuel, that comes into contact with the lens 36.The sensor housing 40 may be made of brass, zinc, aluminum or othermaterial which is non-reactive with the fuel.

FIG. 5 illustrates the fuel sensor 30 positioned below a reservoir 50.The fuel line 35 (FIG. 3A, 3B) or housing 40 may include inlet andoutlet ports 44, 45. During operation, the reservoir 50 may contain apool of liquid fuel. This allows the fuel sensor 30 to be in contactwith mainly liquid instead of being exposed to fuel mixtures that havemore vapor bubbles than liquid fuel. During idle conditions inparticular, the vapor bubble generation in the fuel line 35 may be somuch greater than the liquid fuel 25 coming from the fuel tank 20 thatthe resulting two-phase mixture may erroneously generate a vapor signal.By including the reservoir 50, the denser liquid fuel 25 may settle outto the lowest point in the reservoir 50 while the vapor bubbles passabove this pool off liquid fuel 25. During operation, there will likelybe a mix of some vapor bubbles in this pool, but there will be enoughliquid present for the fuel sensor 30 to detect the liquid state so thata low fuel warning is not erroneously indicated.

The pool of liquid boils away soon after the internal fuel supply tube22 (FIGS. 2A, 2B) starts to draw vapor from the fuel tank 20, sincethere is no new liquid fuel 25 from the tank 20 to replenish thereservoir 50. A higher pressure is required to keep this relativelyhotter liquid pool in the reservoir 50 in a liquid state as comparedwith the system pressure generated by the cooler fuel in the fuel tank20. The tank temperature and resulting tank pressure start to drop morerapidly when the fuel system begins to draw vapor instead of liquid fromthe fuel tank 20. The low fuel indicator 6 (FIG. 1) may be triggeredwhen the fuel sensor 30 identifies that the fuel in the reservoir 50 orin the fuel line 35 is in the vapor state.

FIG. 6 illustrates a fuel sensor 30 located in an auxiliary fuel line65. In one embodiment, the fuel line 35 may be understood as being themain fuel line. The auxiliary fuel line 65 may be connected to and runat a lower vertical elevation than the fuel line 35. For example, liquidfuel 25 traveling between inlet and outlet ports 74, 75 may betransmitted by the fuel line 35 or the auxiliary fuel line 65, or bothlines 35, 65. When the auxiliary fuel line 65 becomes completely full ofliquid fuel 25, excess fuel may pass through the fuel line 35, such thatliquid fuel 25 may be transmitted by both fuel lines 35, 65. Theauxiliary fuel line 65 may allow the denser liquid fuel 25 to pass by orthrough the fuel sensor 30 while the less dense vapor bubbles passthrough the main fuel line 35. During low fuel demands, all the liquidfuel 25 may be transmitted via the auxiliary fuel line 65.

FIG. 7 illustrates the fuel sensor 30 positioned above the reservoir 50.The fuel sensor 30 may described as being inverted, as compared withFIG. 5. The housing 40 may be configured or constructed so as to provideor include the reservoir 50. The lens 36 may be positioned such that itremains immersed in a pool of liquid fuel 25 contained in the reservoir50. Vapor bubbles may be allowed to bypass the sensitive portion of thelens 36, for example in an area of the reservoir 50 that is locatedabove the lens 36. The reservoir 50 may therefore enable separation ofthe fuel vapor bubbles from the liquid fuel 25. In one embodiment, firstport 44 is an outlet port and second port 45 is an inlet port.

FIG. 8 illustrates an alternate embodiment of a fuel sensor 80 attachedto a flexible wire 85. The fuel sensor 80 may be unaffected by themounting orientation of the housing 40 to the fuel line, as the flexiblewire 85 allows the fuel sensor 80 to move around freely inside thesensor housing 40. The fuel sensor 80 settles to the bottom of thesensor housing 40 in order to remain below the surface of the liquidfuel 25 in the reservoir 50. The fuel sensor 80 may be configured tooperate regardless of the orientation of the housing 40. The inlet andoutlet ports 45, 44 may be centered in the ends of the housing 40 so theliquid fuel 25 will pool around the fuel sensor 80. In one embodiment,the fuel sensor 80 is an electro-optic liquid level sensor attached tothe flexible wire 85.

FIG. 9 illustrates an algorithm including a sensor sampling timeinterval for detecting a low fuel condition. During a no-load idlecondition, there may not be a continuous flow of liquid fuel 25 to thevaporizer 110 (FIG. 10), but rather an intermittent flow or two-phasecombination of liquid and vapor. The primary seat of the LPfilter/regulator 14 (FIG. 1) may cycle open and closed during theseconditions, for example once every few seconds, instead of beingslightly open all the time. In some applications, the time interval ofthe liquid fuel discharge cycle from the fuel tank 20 may be severalseconds (e.g. three to six seconds) with a one to three second liquiddischarge duration time.

As previously discussed, vapor bubbles may form in the fuel line 35during operation of the vehicle, rather than the fuel line 35 alwaysbeing full of liquid fuel 25. The fuel sensor 30 or controller 200 mayprovide for an extended sampling time feature having programmableduration (e.g. five seconds) which effectively accommodates this. Thesensor sampling time interval feature may be utilized to minimize excessflickering or sounding of the low fuel indicator 6 (FIG. 1) when theliquid level first starts to fall below the fuel pick-up tube inlet 23(FIGS. 2A, 2B). This feature may also be utilized to command the lowfuel indicator 6 to illuminate, sound, remain off, beep or flash afterengine start-up. An example of the sensor indicator activation logic isshown in FIG. 9.

The algorithm illustrated by FIG. 9 may be a programmable operation,which may be executed by a microprocessor or controller. In oneembodiment, if liquid fuel is present the sensor sampling time intervalis not initiated. However, if vapor is present, then the sensor samplingtime interval is initiated. If liquid fuel becomes present during a fivesecond period, the sensor sampling time interval will reset and willinitiate only when vapor is present again. If vapor is continuous for atleast five seconds, the low fuel indicator 6 (e.g. LED) will beactivated and remain on for five seconds. The next sensor sampling timeinterval may be initiated when liquid fuel is again detected, and thecycle repeats as described above.

A minimum latched interval of the low fuel indicator 6 (e.g. fiveseconds as shown in FIG. 9) may be used to prevent excess flickering.Longer latched periods could reduce the frequency of warning lightactivation. However shorter intervals may give the operator a betterindication of the tank status. For example, if the tank's liquid fuellevel is just starting to fall below the pick up tube inlet 23 (FIGS.2A, 2B), the low fuel indicator light activation may be moreintermittent. If the operator notices a steady activation of the lowfuel indicator 6, it may indicate that the tank 20 is closer to beingempty. In the example shown in FIG. 9, the low fuel indicator 6 neveractivates for less than five seconds. However, if liquid is detectedwithin the five second period, the low fuel indicator 6 is automaticallyturned off at the end of the five second interval (see for examplecondition A at time 10 seconds and condition B at 13 seconds).Significant two-phase conditions or alternating vapor and liquid may notactivate the low fuel indicator 6 unless the vapor phase is of at leastthe minimum threshold duration. For example, in condition C of FIG. 9,the low fuel indicator 6 does not activate until the time indicated at24 seconds.

Longer sampling times may be beneficial in preventing early activationthat may be caused by continuous operation of the vehicle on a slopedsurface, or by extended time between flow intervals at idle conditions.If the liquid fuel discharge interval is approximately eight seconds onsmaller engine applications, the sensor sampling time interval may needto be greater than five seconds especially if the fuel sensor 30 islocated in a section of the fuel line 35 that has a constant vaporpocket.

Auxiliary Fuel Tank System

FIG. 10 illustrates an auxiliary fuel tank system 100 that may beconfigured to be self filling. The auxiliary fuel tank system 100 mayinclude a main fuel tank 115, as well as the battery 8 and engine 15, asillustrated in FIG. 1. In one embodiment, the main fuel tank 115 isunderstood as being a main fuel tank of a motorized vehicle. The mainfuel tank 115 may operate similarly as the fuel tank 20 of FIG. 1. Insome embodiments, the main fuel tank 115 may be removed from theauxiliary fuel tank system 100 or, more generally, the main fuel tank115 may be removed from the vehicle associated with the auxiliary fuelsystem 100. The auxiliary fuel tank system 100 further includes anauxiliary fuel tank 120, vaporizer 110, and LP injector 114. A pressureswitch 126 is shown as being connected to the battery 8, low fuel light128 and low fuel audible alarm 130. A key switch 112 may be providedbetween the battery 8 and the pressure switch 126. The pressure switch126 may be used to indicate when the system pressure is less than somepredetermined threshold value.

The auxiliary fuel tank 120 is illustrated as including end segments124, optional engine coolant flow provisions 122, as well as a reliefvalve V5. An auxiliary valve V1 may be provided between the auxiliaryfuel tank 120 and the fuel line 35. The auxiliary valve V1 may comprisea low back-pressure lockoff valve, checkoff valve, solenoid, or othertype of valve. The auxiliary valve V1 allows fuel to go into theauxiliary fuel tank 120 when the auxiliary valve V1 is open, or in acharged state, or when fuel backflows through the auxiliary valve V1when the auxiliary valve V1 operates as a check valve. When theauxiliary valve V1 is closed, or in an uncharged state, fuel may berestricted from going out of the auxiliary fuel tank 120.

The auxiliary fuel tank system 100 may include a system relief valve V2,a coupling valve V3, a tank valve V4, and lockoff 11. Relief valve V2may be configured to release any excess pressure that builds up in thefuel line 35. Coupling valve V3 may be configured to control or prohibitfuel from exiting the fuel line 35, for example, when the main fuel tank115 is being replaced or is removed. Tank valve V4 may be configured tocontrol or prohibit fuel from leaving the main fuel tank 115 into thefuel line 35. Coupling valve V3 may be included as an integral componentof the fuel line 35. Lockoff 11 may comprise one or more valves thatcontrol or shut off a circulation of fuel through the fuel line 35.Lockoff 11 may be controlled by the auxiliary fuel tank system 100. Tankvalve V4 may be included as an integral component of the main fuel tank115, and may be opened or closed during refueling or replacement of themain fuel tank 115. In one embodiment, tank valve V4 is manually openedand closed by an operator. Coupling valve V3, tank valve V4 and/orlockoff 11 may be separately operated, or operated together, to controlthe flow of fuel from the main fuel tank 115 to the fuel line 35.

The auxiliary fuel tank 120 may include a fuel limiting provision toprevent tank capacity from exceeding more than 80% liquid propane. Theauxiliary valve V1 may be located at the lowest point in the LP fuelline to ensure that liquid propane enters the auxiliary fuel tank 120rather than vapor. This configuration may also be configured toaccommodate a release of liquid propane from the auxiliary fuel tank120.

The auxiliary fuel tank system 100 may be configured for forklifts orother internal combustion powered vehicles that provides a useful amountof reserve fuel after the main fuel tank 115 runs empty. The auxiliaryfuel tank 120 may automatically replenish itself when the main fuel tank115 is refilled or replaced. In one embodiment, a propane vapor sensor,such as the fuel sensor 30 of FIG. 1, triggers the activation of a tankheater 27 (FIG. 1) or activates the auxiliary fuel tank 120 aftersensing a pending low fuel condition.

The auxiliary fuel tank system 100 may be configured to automaticallyfill the auxiliary fuel tank 120 when the main fuel tank 115 isrefilled, or when the main fuel tank 115 is replaced or installed on themotorized vehicle. The auxiliary fuel tank 120 may be filled after apredetermined period of time from when the main fuel tank 120 isrefilled or replaced, In some embodiments, an empty fuel tank may beremoved from the motorized vehicle when it becomes empty, or nearlyempty, and may be replaced with a full, removable fuel tank thatcontains fuel, such as liquid propane gas. Lockoff 11 may be closedwhile the main fuel tank 115 is being replaced, and then reopened toallow the fuel to exit the main fuel tank 115 and then enter the fuelline 35. The motorized vehicle may continue to operate using fuel fromthe auxiliary fuel tank 120, even after the main fuel tank 115 has beenremoved. This may provide the motorized vehicle time to travel betweentwo different refuelling stations, for example.

Auxiliary valve V1 may be opened together with lockoff 11 such that atleast a portion of the fuel from the main fuel tank 115 that enters thefuel line 35 is further allowed to enter the auxiliary fuel tank 120.After the auxiliary fuel tank 120 is full, auxiliary valve V1 may beclosed while lockoff 11 remains open, e.g, during normal operation ofthe motorized vehicle. Lockoff 11 may remain open as long as thereremains a sufficient amount of fuel in the main fuel tank 115 to powerthe motorized vehicle. Auxiliary valve V1 may remain closed as long asthere remains a sufficient amount of fuel in the main fuel tank 115.

When a low fuel operating condition is detected, the auxiliary fuel tanksystem 100 may be configured to close the lockoff 11. Similarly, inresponse to detecting the low fuel operating condition, the auxiliaryfuel tank system 100 may be configured to open the auxiliary valve V1.Auxiliary valve V1 may be open while lockoff 11 is closed. Auxiliaryvalve V1 and lockoff 11 may be opened and closed, respectively, at thesame time, or in sequence. For example, auxiliary valve V1 may be openedto allow fuel from within the auxiliary fuel tank 120 to enter the fuelline 35, and then lockoff 11 may be closed after auxiliary valve V1 isopened.

By controlling the timing of when lockoff 11 is closed, the auxiliaryfuel tank system 100 can help ensure that fuel from the auxiliary fueltank 120 is not allowed to enter the main fuel tank 115, and that themain fuel tank 115 remains empty during the low fuel operatingcondition, so that all of the fuel can instead be used to power theengine 15. An empty main fuel tank 115 also improves efficiency in fuelusage so that the operator of the motorized vehicle is not returning orexchanging a fuel tank that still contains unused fuel.

Staging the opening and closing of the valve V1 and lockoff 11 may alsohelp to ensure an adequate supply of fuel in fuel line 35 withoutstarving the engine 15. The timing of opening and closing auxiliaryvalve V1 and lockoff 11, respectively, may be configured to avoid, orminimize the amount of, fuel from the auxiliary fuel tank 120 fromentering the main fuel tank 115. In some embodiments, lockoff 11 may beclosed prior to the opening of auxiliary valve V1. In still otherembodiments, lockoff 11 may be closed at substantially the same timethat auxiliary valve V1 is opened.

The auxiliary valve V1 may comprise a directional control valve that isconfigured to selectively control the direction of flow of fuel into, orout of, the auxiliary fuel tank 120. When the main fuel tank 115 isbeing refilled or replaced, auxiliary valve V1 may be configured toallow fuel to enter the auxiliary fuel tank 120 and to restrict any fuelfrom leaving the auxiliary fuel tank 120. When the low fuel operatingcondition is detected, auxiliary valve V1 may be configured to allowfuel to exit the auxiliary fuel tank 120 and enter the fuel line 35.

During normal operation of the motorized vehicle, the auxiliary fueltank system 100 may be configured to provide fuel to the engine 15primarily from the main fuel tank 115. During a low fuel operatingcondition, the auxiliary fuel tank system 100 may be configured toprovide fuel to the engine 15 primarily from the auxiliary fuel tank120. The flow of fuel both to and from the main fuel tank 115 may beprohibited during the low fuel operating condition.

The auxiliary fuel tank system 100 may be configured to open and/orclose valve V1 and lockoff 11 in response to detecting a fuel pressure.The fuel pressure may be detected in the fuel line 35, in the main fueltank 115, in the auxiliary fuel tank 120, by pressure switch 126, by apressure sensor, or by any combination thereof. In some embodiments, theauxiliary fuel tank system 100 may be configured to open and/or closevalve V1 and lockoff 11 in response to detecting a low fuel operatingcondition using any system, apparatus, or method of detecting the lowfuel operating condition, as further described in the presentapplication.

In one embodiment, the auxiliary fuel tank 120 is sized for anapproximately 15 minute fuel supply. The pressure switch 126 may beprovided with an initial activation pressure of 20 pounds per squareinch (psi) or less. The low pressure switch 126 may be configured todeactivate at a pressure of 30 psi or more. The auxiliary valve V1 maybe configured to allow fuel into the auxiliary fuel tank 120 when theauxiliary valve V1 is initially in an uncharged position, e.g., when themain fuel tank 115 is being refilled or replaced. The auxiliary valve V1may be configured to allow fuel from the auxiliary fuel tank 120 to bereleased into the fuel supply system when the auxiliary valve V1 is inthe electrically charged position, e.g., when the low fuel operatingcondition is detected. The auxiliary fuel tank 120 may be tee'd into thefuel line 35 upstream of the main fuel supply lockoff 11.

The pressure switch 126 may be activated when liquid fuel is boiled offin the main fuel tank 115 and the supply vapor pressure is low. Inresponse to detecting the low fuel operating condition, the auxiliaryvalve V1 may be configured to open and release fuel from the auxiliaryfuel tank 120 into the fuel line 35. The low fuel warning light 128 andaudible alarm 130 may be connected to the same circuit as the auxiliaryvalve V1, thus warning the operator of the low fuel condition. Thiscycle may continue until the auxiliary fuel tank 120 runs out of fuel oruntil the truck is turned off for refueling. In the event that the truckis turned off during the low fuel operating condition, upon restartingof the truck, the auxiliary fuel tank system 100 may be configured tocontinue providing fuel from the auxiliary fuel tank 120 based on asystem check indicating the low fuel operating condition.

During or after refilling or exchanging the main fuel tank 115 and withthe tank valve V4 and lockoff 11 opened, the auxiliary fuel tank 120recharges until it is full. In one embodiment, the auxiliary fuel tank120 remains full until the pressure switch 126 is activated or theauxiliary valve V1 is opened.

When the main fuel tank 115 is replaced or changed out with fuel stillremaining, the operator may be returning fuel that has been paid for.Providing the auxiliary fuel tank 120 helps ensure this does not happenor, at least, helps ensure that the amount of remaining fuel isminimized. A pressure drop in the main fuel tank 115 or fuel line 35 mayindicated that there is no more liquid fuel left in the main fuel tank115. The auxiliary fuel tank system 100 may be configured to utilize theauxiliary fuel tank 120 to provide additional run time, in response todetecting a low fuel operating condition. In response to detecting ahigher pressure associated with a replacement or refilled main tank, theauxiliary fuel tank system 100 may be configured to switch the main fueltank 115 back into the system. Switching the main fuel tank 115 backinto the auxiliary fuel tank system 100 may operate to automaticallyrecharge the auxiliary fuel tank 120 and resupply fuel to the system.

During the low fuel operating condition, the auxiliary fuel tank 120 maybe open to the fuel line 35 while the main fuel tank 115 is disconnectedor shut off from the fuel line 35. After mounting a full main fuel tank115, the tank valve V4 and interlock 11 may be opened to allow fuel fromthe main fuel tank 115 to flow into the fuel line 35 while the auxiliaryfuel tank 120 is still open to the fuel line 35. The auxiliary fuel tank120 may remain open to the fuel line 35 long enough after the main fueltank 115 is connected to permit recharging of the auxiliary fuel tank120. The amount of time that the auxiliary fuel tank 120 remains openmay be a time function or a sensed function. For example, the auxiliaryvalve V1 may close after a predetermined period of time once the tankvalve V4 and/or interlock are opened, or after a change in pressure isdetected.

After the auxiliary fuel tank 120 is recharged, the auxiliary valve V1may be closed. The auxiliary valve V1 may remain closed while the tankvalve V4 and/or interlock 11 remain open. In response to detecting thelow fuel operating condition, e.g., a low pressure, the auxiliary fueltank system 100 may be configured to reopen the auxiliary valve V1 andreconnect the auxiliary fuel tank 120 to the fuel line 35. During thelow fuel operating condition, the interlock 11 may be closed while theauxiliary valve V1 is open. This allows all of the fuel in the main fueltank 115 to be completely consumed by the engine 15, such that the mainfuel tank 115 is not returned or exchanged with remaining fuel.Detecting the low fuel operating condition and switching operation fromthe main fuel tank 115 to the auxiliary fuel tank 120 may provide foradditional time for operation of the motorized vehicle and/or time toreturn the vehicle to exchange or refill the fuel tanks. Detection ofthe low fuel operating condition using a pressure based detection systemmay avoid false low fuel signals or warnings due to fuel slosh or fueltank orientation.

In one embodiment, the auxiliary fuel tank 120 auto-refills when a fullfuel tank, e.g, main fuel tank 115, is installed or replaced in theauxiliary fuel tank system 100. No operator action may be required toswitch the installed tanks in and out of the system. For example,auxiliary valve V1 and lockoff 11 may be controlled directly by theauxiliary fuel tank system 100. In one embodiment, auxiliary valve V1and lockoff 11 may comprise one or more pressure switches and/orsolenoid lock-off valves.

The auxiliary fuel tank system 100 may incorporate temperaturecompensating pressure switches, to provide detection of a low fuelcondition due to pressure changes for vehicles operating in extremeconditions, such as a freezer or cold room, or in environments withlarge temperature fluctuations. The temperature compensated pressureswitches may be manually adjusted, or self adjusting, depending on themeasured temperature(s). The temperature compensated pressure switchesmay operate or be adjusted based on fuel temperature or ambienttemperature.

The auxiliary fuel tank 120 may be permanently mounted to the motorizedvehicle, whereas the main fuel tank 115 may be removable from themotorized vehicle. The main fuel tank 115 may be removed during arefilling or refueling operation, and then reinstalled on the same ordifferent motorized vehicle in a full condition.

The main fuel tank 115 may completely run out of usable fuel (bothliquid and high pressure vapor) when the low fuel operating condition isdetected. In one embodiment, only relatively low pressure fuel vapor isleft in the main fuel tank 115 when it is exchanged for a new fuel tank.When the main fuel tank 115 runs out of usable fuel, the auxiliary fueltank 120 may comprise a sufficient amount of fuel that will allow thevehicle to continue to run long enough to return to the refuelingstation to refuel and/or change out the main fuel tank 115.

The auxiliary fuel tank may be refilled from the main fuel tank 115without the use of any pumps or additional sources of pressure orvacuum, except for the pressure provided by the fuel in the main fueltank 115. In one embodiment, no action is required to be taken by theoperator to refill the auxiliary fuel tank 120 when the main fuel tankis being replaced or exchanged. In other embodiments, the operator mayenable one or more switches to begin filling the auxiliary fuel tank 120during, or after, refilling or replacing the main fuel tank 115.

FIG. 11 illustrates a relationship of vehicle run time estimations,vapor pressure and ambient temperature of a liquid propane fuel system.The graph demonstrates how monitoring LP fuel level based on vaporpressure cannot provide a consistent or adequate warning time over awide temperature span due to the varying propane vapor pressure.However, if the fuel reserve system is instead based on liquid LPinstead of propane vapor the effect of temperature on run time would nolonger be a significant factor.

The pressure switch 126 (FIG. 10) may be set for 32 psi, to provideapproximately two minutes of warning. However, longer low fuel warningtimes via higher pressure switch settings (e.g. 40 psi and 60 psi) cancause the low fuel light to illuminate regardless of liquid fuel levelin cold conditions. By way of example, a conventional low fuel warninglight will illuminate if temperature is less than ˜38° F. and 60 psiswitch is used. FIG. 11A is a table illustrating example operatingconditions used in the run time estimations of FIG. 11.

The vehicle run time estimations and vapor pressure shown in FIG. 11 aretemperature dependent. The relationship shown in FIG. 11 assumes thatthe tank vapor is at ambient temperature when liquid is below the fuelpickup tube. Once liquid starts boiling off, e.g., when the fuel getsbelow the fuel pickup tube, the temperature in the fuel tank may dropsignificantly, and the tank pressure may also drop quickly. Adding aheater, such as heater 27 of FIG. 1. to the fuel tank may increasevehicle run time.

The auxiliary fuel tank 120 of FIG. 10 provides a predictable low fuelwarning period even during cold weather operation. It may increase thelow fuel warning/operation time which allows an operator to complete atask before returning to the refill station. It may also allow the mainfuel tank 115 to be completely emptied so no unused fuel is wasted whenfuel tanks are exchanged. The audible alarm 130 (FIG. 10) may beincorporated to complement a low fuel warning light 128 to ensure theoperator is aware of a low fuel condition.

The auxiliary fuel tank 120 provides for a longer LP low fuel warningtime which allows equipment operators adequate time to finish a job(i.e. a forklift emptying a delivery truck, etc.) and return to the fueltank exchange station or refueling station before the engine dies. Fuelcost savings may be achieved by running the LP fuel exchange tanks untilnearly empty instead of returning fuel tanks that are partially full.Productivity may be improved since equipment can be operated longer andwith fewer tank changes as compared to methods where the tank is changedout prematurely (based on operator's rough estimates of remaining fuel).Cost savings may be realized by avoiding down time and extra laborassociated with arranging to exchange fuel tanks on trucks that run outof fuel away from the refueling station.

Vehicle Performance Limitation System

Engine performance of an LP fueled vehicle can be limited based on a lowfuel signal and a timer. By including a vehicle performance limitationsystem it may encourage operators not to ignore the low fuel warning(which may be done via engine performance limitation) and instead promptthe operator to refuel the fuel tank 20 (FIG. 1) or the main fuel tank115 (FIG. 10).

The following example uses the algorithm previously described withrespect to FIG. 9. An indicator light or alarm, such as the low fuelindicator 6 (FIG. 1) or 128 (FIG. 10), may indicate a low fuelcondition. Once vapor is detected the sensor, such as the fuel sensor 30(FIG. 1) looks for a five second steady vapor signal. The low fuelindicator 6 remains off until the fuel sensor 30 detects steady vaporfor five seconds. The fuel sensor 30 will look for a five second steadyvapor condition again. If steady, the low fuel indicator 6 remains onand this cycle repeats. If not, the low fuel indicator 6 goes out.

After a five minute steady low fuel sensor signal, the engineperformance may be limited to a first engine speed. For example, thefirst engine speed may be set at 1800 revolutions per minute (RPM). Inone embodiment, the low fuel indicator 6 is commanded to flash or soundon and off at alternating one second intervals. After a ten minutesteady low fuel sensor signal, the engine performance may be limited toa second engine speed less than the first. For example the second enginespeed may be set at a maximum value of 1200 RPM. The low fuel indicator6 may be commanded to flash or sound on and off at alternating one halfsecond intervals. Engine speeds and time intervals may be programmable.

The low fuel indicator 6 may be provided in a vehicle dash, or providedas part of an aftermarket system. It may also be used for activating anaudible alarm on Aftermarket or Original Equipment Manufacturer (OEM)systems. To avoid operator disablement of the low fuel indicator 6, ifthe engine 15 is turned off during either of the five minute or tenminute intervals, the system memory may accommodate restart at thetiming cycle where it stopped. The cycle may be reset if the fuel sensor30 no longer provides a steady signal, such as when the fuel tank 20 isbeing refueled. If the vehicle was shut down during either of the fiveminute or ten minute intervals, upon restart, the system may wait forshort period of time (e.g. seven seconds) before looking for a low fuelinput signal. If a low fuel signal occurs within seven seconds afterstart up, the system timer may need to start at the same place it wasstopped. If not, the entire cycle may be repeated.

In one embodiment, the engine performance may be reduced by 50% aftersome period of time (e.g. five minutes) after a low fuel warningcondition is identified. An idle performance (creep speed) of the enginemay be commanded some ten minutes after a low fuel warning condition wasidentified. This encourages the operator to go refuel the truck beforethe engine stalls due to lack of fuel.

The vehicle performance limitation system may be configured to pick upengine speed via inductance from a spark plug wire and control a valvein the fuel line 35 that is either plumbed into the system or integratedinto the fuel sensor 30 itself. Since this valve is only operationalduring the vapor mode, engine speed control problems associated withliquid fuel droplets boiling off vapor in an uncontrolled fashion areeliminated.

FIG. 12 illustrates a example method of monitoring a low fuel conditionin a motorized vehicle. The method may be performed by a microprocessor,computer, processor or the controller 200 shown in FIG. 1. At operation210, signals are received from a fuel sensor, such as fuel sensor 30 ofFIG. 1. The signals may indicate the presence of a vapor, a liquid, or atwo-phase combination of vapor and liquid in a fuel line.

At operation 220, the number of signals received from the fuel sensor 30is determined. The number of signals may be used by an algorithm, asdescribed with respect to FIG. 9 for example, and including a sensorsampling time interval.

At operation 230, the low fuel condition is identified when the numberof received signals exceeds a threshold value. In one embodiment, thelow fuel condition is identified when a number of signals is receivedthat correspond to a five second period of time.

At operation 240, a vehicle operator is alerted to the low fuelcondition. The operator may be alerted via a low fuel indicator light oraudible alarm.

At operation 250, a low fuel mode of operation of the motorized vehicleis commanded. The low fuel condition may indicate the presence of a fuelvapor in a fuel line.

In one embodiment, a low fuel control valve may operate to control thefuel vapor only during the low fuel mode of operation.

At operation 260, an engine speed of the motorized vehicle is restrictedto a maximum operational value in the low fuel mode of operation. Atoperation 270, an engine starter is disabled when the low fuel mode ofoperation is completed.

In one embodiment, the weight of the fuel tank 20 mounted to anindustrial vehicle is compared to the weight of an empty fuel tank inorder to determine the amount of remaining fuel in the fuel tank 20. Theweight may be determined by a sensor, for example. A low fuel conditionmay be identified when weight of the fuel tank 20 approaches the weightof an empty fuel tank.

In another embodiment, a temperature differential between a liquid andgaseous (ambient) section of the fuel tank 20 is measured to determine afuel level. For example, an upper sensor, or first thermistor, may belocated near the top of the fuel tank 20, and a lower sensor, or secondthermistor, may be located near the bottom of the fuel tank 20. In oneembodiment, the lower sensor is located at approximately 10% of the fulltank level. The two sensors may be attached to a tank clamp. A low fuelcondition may be identified when the temperature differential approacheszero or some other threshold value, or when the upper and lower sensorsdetect the same value.

The fuel sensor 30, 80 may be used for other types of fuel besidespropane. Other fuel sensor types and vapor/liquid detection systems andmethods may be used with the systems and method described herein. Thesensors may include: ultrasonic, acoustic, catalytic, thermal, optical,infrared, photoelectric, electrochemical, mechanical, tank temperaturedifferential, semiconductor, vibrating, di-electric constant, and flowvelocity comparisons of the fuel.

FIG. 13 illustrates a further embodiment of an auxiliary fuel tanksystem 300. Fuel line 335 includes a first end 310 configured to receivefuel from a fuel tank, such as fuel tank 20 (FIG. 1) or main fuel tank120 (FIG. 10), and a second end 330 configured to transmit fuel to anengine, such as engine 15 (FIG. 10). Auxiliary fuel tank 320 may containone or both of liquid fuel 350 and vapor fuel 340. The liquid fuel 350may comprise liquid propane gas. In one embodiment, the auxiliary fueltank 320 may be configured to store no more than 80% liquid fuel byvolume, or as determined by regulation or engineering standards, toprovide an expansion area, e.g., 20% by volume. A vent line 365 may beconfigured to maintain a predetermined ratio of the liquid fuel 350 andvapor fuel 340 within the auxiliary fuel tank 320.

A first valve 360 may be configured to receive fuel from the fuel line335. First valve 360 may provide means of filling the auxiliary fueltank 320. The first valve 360 may allow fuel to flow to the auxiliaryfuel tank 320 when it is activated. In one embodiment, the first valve360 acts as a one way check valve when the first valve is not activated.The first valve 360 may allow fuel to enter the auxiliary fuel tank 320anytime it was not full. A reduced pressure differential or backpressure, e.g., less than 20 psi, associated with first valve 360 mayfacilitate refilling of the auxiliary fuel tank 320. First valve 360 maybe electrically actuated. For example, first valve 360 may be activatedbased on a detected system pressure, on a time control, or be manuallyactivated.

The auxiliary fuel tank 320 may comprise a second valve 390 positionedat or near the bottom end of the auxiliary fuel tank 320. Providing thesecond valve 390 on the bottom of the auxiliary fuel tank 320 maypromote better fuel flow to the engine. The second valve 390 may beconfigured to allow fuel from within the auxiliary fuel tank 320 toenter the fuel line 335 via auxiliary fuel line 395. In one embodiment,both of the first and second valves 360 and 390 may be opened at thesame time while the auxiliary fuel tank 320 is being filled. Theauxiliary fuel tank 320 may be filled during operation of the vehiclefor some period of time, e.g., a number of minutes, after a refuelingoperation is completed, or during the refueling operation.

Accumulators and/or mechanical float valves (not shown) may beconfigured to shut off one or more of the first and second valves 360,390 once the liquid fuel 350 reaches a predetermined level.

The system and apparatus described above can use dedicated processorsystems, micro controllers, programmable logic devices, ormicroprocessors that perform some or all of the operations. Some of theoperations described above may be implemented in software and otheroperations may be implemented in hardware.

For the sake of convenience, the operations are described as variousinterconnected functional blocks or diagrams. This is not necessary,however, and there may be cases where these functional blocks ordiagrams are equivalently aggregated into a single logic device, programor operation with unclear boundaries.

Having described and illustrated the principles of the invention in apreferred embodiment thereof, it should be apparent that the inventionmay be modified in arrangement and detail without departing from suchprinciples. I claim all modifications and variation coming within thespirit and scope of the following claims.

1. A fuel system for an engine, comprising: a fuel line configured todeliver fuel from a removable main fuel tank to the engine; a firstcontrol device configured to release a flow of the fuel from the mainfuel tank into the fuel line; an auxiliary fuel tank connected to thefuel line; and a second control device configured to control a flow ofthe fuel between the auxiliary fuel tank and the fuel line, whereinafter the fuel is released from the main fuel tank into the fuel line,the second control device fills the auxiliary fuel tank with the fuelfrom the main fuel tank.
 2. The fuel system of claim 1, furthercomprising a pressure detecting device configured to detect a systempressure, wherein the second control device automatically releases aflow of the fuel from the auxiliary fuel tank into the fuel line inresponse to the pressure detecting device detecting a decrease in thesystem pressure.
 3. The fuel system of claim 1, wherein the secondcontrol device is configured to prohibit a release of the fuel from theauxiliary fuel tank into the fuel line while the fuel is being deliveredfrom the main fuel tank to the engine.
 4. The fuel system of claim 1,further comprising a low fuel detection device configured to detect adecreased amount of fuel in the fuel system, wherein the second controldevice is configured to release a flow of the fuel from the auxiliaryfuel tank into the fuel line in response to the low fuel detectiondevice detecting the decreased amount of fuel.
 5. The fuel system ofclaim 4, wherein in response to the low fuel detection device detectingthe decreased amount of fuel, the first control device is configured toprohibit the flow of the fuel both from the main fuel tank into the fuelline, and from the fuel line into the main fuel tank, and wherein thefuel line is configured to deliver the fuel from the auxiliary fuel tankto the engine.
 6. The fuel system of claim 5, wherein the main fuel tankis substantially empty of the fuel while the fuel is delivered from theauxiliary fuel tank to the engine.
 7. The fuel system of claim 4,wherein the first control device is configured to release the flow ofthe fuel from the main fuel tank into the fuel line prior to thedetection of the decreased amount of fuel.
 8. An apparatus, comprising:means for delivering fuel from a main fuel tank to an engine; means forreleasing a flow of the fuel from the main fuel tank into the means fordelivering; means for storing an auxiliary fuel supply; means forcontrolling a flow of the auxiliary fuel supply between the means forstoring and the means for delivering, and means for filling the meansfor storing with the fuel from the main fuel tank after the flow of fuelis released from the main fuel tank into the means for delivering. 9.The apparatus of claim 8, wherein the means for controlling isconfigured to release the flow of auxiliary fuel supply into the meansfor delivering based on a predetermined period of time after the flow offuel is released from the main fuel tank.
 10. The apparatus of claim 8,wherein the means for controlling is further configured to prohibit arelease of the flow of the auxiliary fuel supply into the means fordelivering while the fuel is being delivered from the main fuel tank tothe engine.
 11. The apparatus of claim 8, further comprising a means fordetecting configured to detect a decreased amount of fuel in the fuelsystem, wherein the means for controlling is configured to release theflow of the auxiliary fuel supply into the means for delivering inresponse to the detection of the decreased amount of fuel.
 12. Theapparatus of claim 11, wherein in response to the detection of thedecreased amount of fuel, the means for releasing is configured toprohibit the flow of the fuel both from the main fuel tank into themeans for delivering, and from the means for delivering into the mainfuel tank.
 13. The apparatus of claim 8, wherein the main fuel tank isconfigured to supply the fuel to the engine during a first mode ofoperation, and wherein the means for storing is configured to supply theauxiliary fuel supply to the engine during a second mode of operation.14. The apparatus of claim 13, wherein the first mode of operation isassociated with a normal operation of the engine, and wherein the secondmode of operation is associated with a reduced level of operation of theengine.
 15. A method, comprising: delivering fuel from a removable mainfuel tank to an engine; releasing a flow of the fuel from the main fueltank into a fuel line; controlling a flow of the fuel between anauxiliary fuel tank and the fuel line, and filling the auxiliary fueltank with the fuel from the main fuel tank after the flow of fuel isreleased from the main fuel tank into the fuel line.
 16. The method ofclaim 15, further comprising detecting an installation of the main fueltank onto a vehicle, wherein the flow of the fuel from the fuel lineinto the auxiliary fuel tank is controlled in response to detecting theinstallation of the main fuel tank.
 17. The method of claim 15, furthercomprising prohibiting a release of the fuel from the auxiliary fueltank into the fuel line while the fuel is being delivered from the mainfuel tank to the engine.
 18. The method of claim 15, further comprisingdetecting a removal of the main fuel tank from the fuel system, whereinthe flow of the fuel is released from the auxiliary fuel tank into thefuel line in response to the removal of the main fuel tank.
 19. Themethod of claim 18, wherein in response to the detection of thedecreased amount of fuel, the flow of the fuel from the main fuel tankinto the fuel line is prohibited, and the flow of the fuel from the fuelline into the main fuel tank is prohibited.
 20. The method of claim 18,wherein the fuel line is configured to deliver the fuel from theauxiliary fuel tank to the engine, and wherein the main fuel tank issubstantially empty of the fuel while the fuel is delivered from theauxiliary fuel tank to the engine.